| 年度 | 实际值 |
|---|---|
| 1995 | 26.1 |
| 1996 | 26.9 |
| 1997 | 28.61 |
| 1998 | 29.5 |
| 1999 | 26.4 |
| 2000 | 22.8 |
| 2001 | 21.14 |
| 2002 | 22.59 |
| 2003 | 25.14 |
| 2004 | 27.07 |
| 2005 | 25.47 |
| 2006 | 24.17 |
| 2007 | 23.79 |
| 2008 | 23.3 |
| 2009 | |
| 2010 | 24.77 |
| 2011 | 25.62 |
| 2012 | 25.2 |
| 2013 | 25.4 |
| 2014 | 24.31 |
| 2015 | 22.76 |
| 2016 | 21.24 |
| 2017 | |
| 2018 | 17.72 |